Electric braking.



TUNITEDTSTATES PATENT ALEXANDERsoN, or' SCHENECTADY, NEW Yon-K,` Assiettes 'ro GENERAL ELECTRIC contraint,V A comonA'rroit ornrnvv YORK.. ,u

ERNST. r. lW.

'To 'all whom'it may concern.'

f Be it known-that' I, ERNST F. W. ALEX- t. ANDERSON, a citizen of the United` States, re-

more. stable condition when the motors are,l

Vto the source.

-otherwise obtainable.

connected as bra king generators.

It has been proposed. heretofore, in the case of a plurality of series motors connected to drive a common load, to employ one of the motors as a separately-excited generator driven by the load, 'and to use it to excitev thetield of another motor, which acts as a braking generator driven by the load to return power to the line. y

My invention, in one aspect, consists in superposing 'on the excitation derived from the first motor an opposing excitation proportional to the current returned to the source. In 'other Words, the motor which returns energy to the source is excited differentially by the current generated in the excitingmotor `and by thecurrent returned This differential excitation results in more stable conditions than are For instance, if the motor ata given speedA is lreturning a certain amount of energy to the line and thus acting as a brakingl generator to-decrease the speed, then when the speedfalls, the induced voltage of this motor tends to fall,

and the current returned to the line tends to decrease; but with the differential excitation which I employ, this decrease of current returned to the source increases the field excitation of the ymotor or braking generator, so that the effect of the reduced speed on theinduced voltage is partly offset.

The differential excitation may be obtained by connecting the field winding of the kbraking generator in Whole, or in part, in series Withits armature. i

Myinvention, as set forth above, is applicable both to direct-'current aindfto alternating-current motors. Then applied to alternatingcurrent motors, however, the inclusion of the exciting Winding in the armature circuit results-1n an advantage 1n ad- `ing of the braking-generator.inits r`m that would be produced if the whole' lerici ELECTRIC BRAKING.

Specification of Letters Patent. Pateiifd 19ML Appui-.aubufued February 19,1 190s. serial in.` 416,695., v

dition to and apartffroniimproving the characteristic of thek brakingfgenerator.' l"- Then one,alternating-current motor is'eni'- ployed to Aexcite another `in the manner-l above set forth, the phase relations of the f 6o currents andvoltages in the two'niotorsaref: as follows: On the 'exciting winding ofthe motor which ser 'es as exciter,a 'voltages4 is impressed ifn phase with the voltage :of''the' source i g v l y y Since the exciting winding is highlyiin; i: ductive, the exciting current, and conse-1y quently the induced voltage in the armaturef` vof the ,motorlu'hich servesas. an exciter,; is'

substantially in quadrature with the voltag .J of the source. .This induced voltage-is inipressedy on the exciting Winding-of the moe tor which ser-ves as a braking generator, and:

vconsequently the current .in ,they exciting winding of this latter motor, and, therefore, its induced-armature voltage, are in phase with, or rather, in opposition to, the voltage of the source. It', however, the ,induced voltage of the braking generator isexiactly in oppositionto the voltage of the'source, so H80 that'the resultant of thesey two-voltages isitself exactlyin opposition to the `lvoltage of the source, no energy .will be returned tothe source, since the circuit formed by the braking generator andthe sourceis highly in,- ductive. and the current lags nearly ninety degrees behind the voltage. The current l. that would flou in this case would, therefore, be Wattless.l In orderv that'fenergy may be.

' returned j to t-he source, the voltagey at thev 90 terminals of the braking generator should.,` be nearly, but not quite, in opposition ,to .gij the voltage ofv the source, so that the ,rey sultant of these two voltages vmay be apl .f proxnnately ninety degrees out of Lphase..9, 5 with thevoltage of the source. Vith this.,M

condition, the current which is returned tof;

the source in opposition 4to thevoltage ,of the source;-y and 1s coiisetpiently an en" g current. The presence of the exciting Wln ture circuit serves to produca; the'lne'ces small phase-displacement between the tage at the terminals of the braking genera,

tor and the voltage'of the source. Y,

l In manycases the phasedr placement ing winding were included in the armature circuit of the braking generator would be too great. In such a case a part only of -ilie exciting iginding may be included inV thiscircuit, and they connections whereby the exciting winding is included in the 'armature circuit 1n part only may be made directly or' .the exciting winding vof =the braking generaaov ,-toris included only, inpart in the armature circuit; and FigQB shows diagrammatically `a control system for operating thetfwo 1no tors, as motors for driving a load, or as generators lfor braking electrically; and F ig.'v y

4 is an explanatory diagram.

In the drawings, A and A"represent the armatures, B and B the exciting windings, and C and C the compensating windings of a pair of compensated series motors.'` Vhile my invention is not limited to this' particular type of motor, I have selected i'tffor the purpose of illustration,v as it is wellv known in the art. lEach compensating winding'is connected permanently in series with its armature, and in order to avoid the use of unnecessary words, mention of the compensating windings will hereinafter be omitted; the term armature, being usedto include both armature and compensating windings, 'if compensating windings are employed.

In .the drawings the( motor .whose armature is represented by A is employed as an exciter, andthe motor whose armature is represented by, "A, for a braking generator. The" winding B of the exciter-motor, is separately excited by .connecting it "across a portion of a transformer D connected'to the supply mains E E. The voltage impressed on this Winding B is consequently in phase with the voltage of the line. Thecurrent in winding B, and, therefore, the induced Voltage in armatureAare substantially inquadi'ature'with the voltage of the source; This voltage is impressed on the exciting Winding B of the othermotor. The current in winding B and the voltage induced in armature A are, therefore, approximately in phase with, or rather in opposition to the linevoltage. The current which is returned from the armature A to the line passes through the exciting winding B', since this winding is included in the armature circuit. Since `this winding is highly-inductive, its presence in the armature circuit results'in slightly displacing the phase of the armature voltage from the voltage of the line, so that the resultant of these two voltages is practically at right-angles toV the line-voltage. The three voltages might be represented by a right-angle triangle, in which `presse j on 'the winding ltage o a.

which is returned .to the line i8 @tibet-airl tially in quadrature` with the resultant; vole `tage, it is in opposition to the Voltage t er the souree,o r, in other Words, is an e" understood by reference toFig. which o c re nesents the phase of the voltage iinwhich serres as anlexeiter.. The cnrrentin ythis winding 1s represented by c .a lagged nearly ninety degrees behix'ndthe voltage,- and thevoltagelndieed in l ture A in l'phase with the @iX-citan is current. These pliase relations will best e .B of the "motor,

pressed von winding b13` of the braking gein i crater, and ,produces in this winding the .current o d, which 'lags nearly .ninety Vdegrees behind the impressed voltage Q e. vThe 'voltage induced nannature 'is in phase with the current o a?, and may be represented by o e, which isv displacedl nearly but not quiteone hundred and eighty degrees from the line voltage o c. The resultant of thel two voltages c a and 0 e, which represents the voltage drop across the exciting winding B is represented by 0 f, which,4 with the line voltage o a and the voltage o e induced in the armatureAyof the braking generator, forms a right-angle triangle. The current returned to the line is substantially in quad rature with the `resultant voltage-o f and substantially in p'liase with the linevol- As motors are ordinarily designed, the phase -displacenient produced by the presence of the exciting winding B 1n the armashould bey included in the armature circuit. If it is not conveniei'it to bring out an intermediate tap from tlie winding for this purpose, the same-result. may be obtained by the use oi' a small compensator connected as shown in -F igl. tIn thisvfigure the motors are supplied `fronrthe line through a ltransformer I", and the connection to this transformer from the armature A', when the motors are connected for braking, is iliade through a portion ot' a' compensator G,

-Whicli connected in shunt to the exciting windingv B` This connectionhas precisely the same eii'ect electrically as would a connection to the transformer F from an intermediate point o'n the exciting winding itself, and is in effect connecting the exciting winding iii part only in the arn'nit-ure circuitand may be employcdwlieu is not convenient to bring out an intermcduite ytap on that winding. 'Ihebraking eflect in Fig. 2 may be varied both by vai-ying the.

amount of the voltage impressed on the eX- ture circuit may be too great. 4If this is the. case` only-a poitionof the exciting winding "at which time the minimum voltage impressed on the excitiiigiwinding B, while the braking generator is `coiiiectcd across the Whole of the secondary winding ot' ytransformer Fl.

'n Fig. 3 is shown diagrammatically 'a .s-siinple. control s 'vsteiii for the motors with a controllingswitch' ll arranged to connect the motors both as iiiotor.'-iA and for electric braking. rlhis switch H. isishown conventionally `'with vits contacts `developed on' a plane surface. Threeiruniiing positions are shown, indicated by the dotted lines l, 2 and- 3, and three braking positions,indicated by dot-tedlines 1, 2 and 3. When the switch H is moved into one of its running positions, the two motors are connected in series With eachother, and to theisecoiidary ot transformer Ff The only change that is `made iii moving from one ruiming kposition to another is varying `the 4amount of the. voltage impressed oii the motors. It-Will, ,of course, be understood that `this control is used merely `for the purpose of illustration, and Hforms no part ot' `my invention, `and that the Ubiaking 1'coiii'i'e'ctions may be employed in combination ,with any ruiming connections.

f pensate for the reduction in induced voltage In moving to the first braking position l', the connections shown in Fig. 2 are established. Thesev connections, as has been said, are those for braking at. maximum speed. In moving-.to position 2), the voltage iinpressed on exciting Winding B, from 'transformer D, is increased, and the point of connection from the braking generator to 'transformer E is shifted .so as to connect .-i-t across a. smaller number of turns.l This, -iii effect, changes the ratio ot' transformation. of the transformr F so as to comintl-ie motors, dueto decreased speed.' In passing to position 3 the voltage impressed on Winding B is again increased, and theV connections of the braking generator are again ,varied to connect it across a 'still sinallernu'mber of secondary turns of transformer F. Viith each of these braking Vconnections the current returned to the source generator opposesin the exthe'exciter-motor. The result Iis to .give something of a series character,-'that is, to

.. tend to return lto the line a constant current with varying speed, as has been lhere-a tofore explained; and, therefore, vto gire` a.

, stable braking characteristic.

YVhile for the sake ofI simplicity l have shown only two motors in the drawings, it will be understood-.thatmy invention is applicable to any number of motors arranged The connections sliou'ii in Fig.

re lto Vsecure Letters Patent of the United `lStates, Y

l. The method of .braking i systems employing a plurality of; motors Lof the commutator type adaptedtogdriyefa mamon load, which consistsincliner-ating@ portion of the motors asseparatelynexcited lgenerators driven bythe load,.a1 id l )peirl'at-l ing other of said motors as|` generators driven by the load andfexciteldi eren'tially Iby current generated "in gtherstirhnnied l portioiiof the motors and. by,the. ,currient generated by said other.offtlieniotiors.,

2. The method of brakingl systems employii'ig a. plurality ofniotorsof the commutator type adapted" towd a portion of the motors`r as 'generato r's''driveii by the load andexcited."from;tliesourceof current supply, andoperating othe'roi' said motors as generators .drivencby the loadto return power to saidA source,`the latter porcommon load, whiclrconsists,infoperatinga tion of the motors beingfexcitd dilferen`- tially by the current ygenera,tedI in the vfirstmeiitioned motors and'bythe ,current`- ref turned to the source.

3. The method of braking l systems employing aA ,plurality` of` nio'tors "of the coinmutator typev adapted to drive a common load, which consists infop'e'rat. one-of the motors asa generator driven-'by rent, supplying current'il'rom its armature to excite another motor`,"re`tiirning" rrei'it' from the armature ofthe otherniotoi to'fthe source, and superposing `on` the excitation of said other. motor an opposing* excitation proportional to they-'current vreturned ltoi the source. f e l 4. The me hod of braking electricallyfin systems employing a pluralityofmotors'of the eommutator type' adapted f to t"drivei'a 'common load, which consists in operating one of the motors'as a generatordrivenby the load and excited froml'tliefsource 'o-.ciirrent, supplying current from lits varmature fto excite another inotor,'= returningfcurrent from the armature of`tlie-otlier niotorfto the source, superposingon thevekcitationof said other motor an opposingexcitation proportional y to the current rreturned@:tofthe source, and varying theiield-strength of the; first-mentioned motor.

5. Themethod of braking.electricallyjiin systems employing apluralityof' n'fiotorsiof the commutator type adapted to drivelffa common load and supplied fromv altermating-'current sourcethrough .a trans former, which consists in .operating one of the motors as a generatordrwenfby fthe .'lload, and excited -from said source, supplying current from its armature to excite an other-motor, returning current from the armature4 of theother motor tothe -source f5 -through the transformer, superposing on the excitation of saidiother motor an oppos- .ing excitation proportional 4to the current -rcturne'd to the source, and varying the -points of connection of said other motor to' former, superposing on the excitation of saidv other motor an opposing excitation proportional to the current returned to the source,

formation of said transformer.

7. The method of `braking electrically in s stems employing a plurality of motors `of t e commutator type adapted to drive a common load, which consists in operating one of the motors as a separately-excited generator, supplying current from its armature tol ex- .citeanother motor, and operating the latter motor as a braking generator driven by the load to return energy to the source with its exciting winding included at least in lpart in.

its armature circuit.

8. The 'method of braking electrically in systems employing a plurality of alternating-current motors of the commutator type adapted to drive 'a common load, which consists in operating one of the motors as a generator driven by the load and excited by a voltage impressed on its exciting Winding substantially in phase with the voltage of the source so as to produce an induced armature lvoltage substantially in quadrature with the voltage of the source, impressing saidlinduced armature voltage on the-excitduce therein an induced armature voltage substantially -in phase 'with the voltage of the source, and connecting the armature of the other motor tothe source through a part of said exciting Winding in the armaturev circuit serving to produce a small phase dis'- placement between the voltage at the terminals of the motor circuit and the voltage of the source. 1

9. The methodv of braking yelectrically in systems employing a plurality of alternating-current motors of the commutator typel adapted to drive a common load, Which conV and varying. the effectiveA ratio of trans" ing Winding'of another motor so as to pro'-` at least of its exciting Winding, the presence' alternating-current. motors of .the commutasists in operating one of the motors as agen- 'erator driven theload excited by a voltage impressed on its exciting Windmg substantially in phase with the voltage of the source so as to produce an induced armature voltage substantially in quadrature with the voltage 'of the source, impressing said induced armature voltage on the exciting Winding of another motor so. as to produce therein an induced armature .vol-' tage substantially inphase Withlshe voltage of the source, and connecting thel armatureof the other motor to the source through connections including means adapted' to prolduce asmall phase displacement. between substantially in phase with the voltage of the sou-ree so as to produce an induced'armature voltage substantially in quadrature with the voltage `of the source, impressing said induced armature yvoltage on theexciting winding of another motor so as to pro duce therein an induced armature voltage ,substantially in phase with the voltage of 'the source, and connecting the armature of the other motor to the source through a part at least of' a winding which is in circuit with the armature of the first-mentioned motor. l' 1l. In combination With a plurality o f motors of t-he commutator type adapted to drive a common load, a sourceof current therefor, and means for controlling' the motors for electriczbraking, comprising connections for separately exciting one of said motors, means for connecting the armature of said motor to the exciting Winding of' another motor, and means for connecting the armature Winding of the other motor to theV source through a part at least of its exciting Winding. 4 12. In combina-tion Witha plurality-"of` motors of the commutator type. adapted to drive a common 'load, a source of current therefor, and means for controlling the motors for electric braking, comprising connections for separately exciting one of said motors, means for connecting the armature of said motor to the exciting Winding ofl another motor, means for connecting the. armature' Winding of the'other motor to the source through a part at least 'of its eXcitin Winding, and means for varying the iieldg strength of therst-mentioned motor..

13. In combination with a Aplurality of tor type adapted to drive a common vl')a ,"'a ,transformer for supplyingl current to to the transformery through part at least of.

itsexciting Winding.

14.' In combination withl a plurality of alternating-current motors of the commutator type adapted to drive a common load, a transformer for supplying current to said motors,and means for cont-rolling the motors for braking electrically, comprising connections for separately exciting one of said motors, means for connecting the armature of said motor to the, exciting-Winding of the other motor', means for connecting the armature Winding of the other motor to the transformer through a part at least of its exciting Winding, and means for varying the points of connection to said transformer.

l5. In combinatlon with a plurality ot motors of the commutator type adapted to drive lav common load, a 'source oi current therefor, and .means for controlling the motors for electric braklng, comprising con-v nections for separately exciting one of the motors, ineens tor connectingV the armature 30 of said motor to the exciting'vfinding of the other motor, an impedance arranged toA be connwled in parallel with said exciting winding, and connections from the armature ot' tlnI latter motor to the source includinga 35` portion of the parallel circuit formed bytsaid exciting Winding and in ipedance.l

1G. In combination With a plurality of alternating-current motors of'the commutator type adapted to drive a common load. n40

source of current therefoig'and means or vcontrolling the motors for electric braking,

comprising connections for separately excitfv ingone of the motors, means for connecting the armature ot said motor to the'exciting -45 winding of another motor, a lcompensator connected in parallel with said :exciting winding, and connections from the armature ot' .the latter motor to the source including a portionof said compensator whereby said 50 exciting' Winding is in effect partly included in the armaturecircuit.

In" witness whereof, have hereunto set my hand'this 17th day of February, 1908 ERNST F. W. 'ALEXANI)ERSON. lVitnesses:` l

'BENJAMIN B. HULL, HELEN ORFoRD. 

